I'd second Osprey, got a 25l bag I use for much the same thing. Had it for years and it's been all over the world and properly abused. The zip broke apart recently, sent it back with minimal fuss and it was fixed in a day. The only thing that's worth noting though is that their warranty varies a lot by region. If you're in the US you're sweet. But I'm in the UK and heard they can be a bit funny about repairing certain types of damage in Europe and elsewhere.